The manufacture of semiconductor wafers involves the formation of layers, one atop another, on a semiconductive substrate. Each layer is formed as thin film having portions which are then etched away to produce surface relief patterns. These patterns constitute the electronic components of integrated circuits, and are the result of the complex manipulation of layers and impurities which are diffused into sections of the wafer. An important part of this manufacturing process involves the use of photosensitive liquid called photoresist, which is deposited evenly on the semiconductor wafer, then baked to harden the substance. Patterns are defined on the surface using a mask, exposing with ultraviolet light, then chemically developing the exposed photoresist. Industry commonly uses several types of equipment for these processes, each addressing a single step in the manufacture of silicon wafers.
The treatment of wafers coated with resist, and exposed with a circuit pattern, involves employing a resist developer; usually an ammonium hydroxide solution. This basic solution selectively removes the acidic exposed areas of the photoresist. The wafer is sprayed with water to rinse away the developer, then spun rapidly to throw off the water, drying the surface.
A piece of equipment used in subsequent steps is an oven for baking the wafers. This process hardens the developed photoresist so that it will stand up to later, more aggressive, processing steps aimed at underlying layers. These later steps might include treatment by gaseous reactive ion species, commonly referred to as plasma etching, or further processing with wet chemicals. Each of these steps is typically performed independently, in machines designed for a dedicated task.
Spin-spray processing units for photoplates and wafers are known. For example, U.S. Pat. No. 4,161,356 discloses a spin-spray processing unit primarily for photographic plates, but could easily be adapted for wafers. The etching which takes place in this patent is chemical etching. In many processing steps, plasma etching is a preferred method.
In U.S. Pat. No. 4,992,136 Tachi et al. disclose a dry etch plasma method wherein a film forming gas reacts with a surface to be etched, making possible precise etching of complex surfaces, such as the side walls of a hole.
In the past, a collection of spin-spray processors, plasma etchers, and other semiconductor manufacturing equipment occupied a considerable amount of space in wafer fabrication facilities.
An object of the invention is to devise a machine for carrying out the chief functions in the processing of semiconductor wafers within a compact space. It is also an object of the invention to meet requirements for new techniques in plasma resist stripping. These requirements involve the use of wet units to remove either the ash created by plasma processing of the wafer or to remove a thin layer of contaminated photoresist left after partial plasma stripping.